I’ve seen a lot of questions asking about the difference between a line editor and a copyeditor. Although I’m oversimplifying a bit, a line editor will actually rewrite your content whereas a copyeditor typically will not. There are other areas where a copyeditor excels.

Copyeditors ensure consistency with the house or preferred style guide, dictionary, and internal consistency (or factual, in nonfiction works). They go beyond a proofreader by looking at things that, while not grammatically wrong, may confuse or annoy the reader.

One popular example is the word "gray" or "grey." Most dictionaries and style guides equally recognize both spellings. Unless the publisher specifies, it'll be up to the author how it's spelled. But, sometimes authors can be inconsistent.

Many copyeditors have a checklist of things to look out for beyond spelling and punctuation conventions. Of course, every editor has their own list, and lists may differ per author, publishing house, or project, but here are a few examples you’re likely to see on every list.

• Inappropriate verb tense shifts
  • This is most common when the writer is working in the present tense. We’re used to stories being told in the past tense so it’s easy to slip up.
• Multiple sentences in a row starting with the same word
• Sentences lacking parallelism
  • “I like to pet my cats and watching Law & Order.” vs “I like to pet my cats and watch Law & Order.”
• Overuse of adverbs modifying weak verbs
  • Instead of “She spoke quietly” or “He walked very quietly” a copyeditor may suggest “She whispered” or “He crept”. For cases like “She whispered quietly” see the bullet on textual redundancy.
• Inappropriate use of the word “suddenly”
  • It’s tempting for newer authors to rely on “suddenly” to startle or surprise the reader, but much more effective to get right into the action.
• Overuse of expletive sentences
  • Sentences that start with “There is” or “There are”
• Overuse or inappropriate use of the passive voice
  • This is a complex and highly subjective matter. I want to go on record as saying that the passive voice doesn't bother me nearly as much as many copyeditors. In academia, or when the focus of the sentence shouldn’t be on the subject, the passive voice is often preferred.
• Using quotation marks for emphasis
  • I’m not sure when people started doing this or why, but I find it an especially baffling quirk.
• Acronyms without clarification (unless they have been generally accepted as words or are widely known)
• Jargon (unless appropriate for the audience level or purposefully used for characterization)
• Overly long sentences or paragraphs
• Textual redundancy
  • “She nodded her head” would become “She nodded” because, under normal circumstances, you can’t nod anything other than your head.
• Awkward text

Everyone’s heard those three ubiquitous words before. It seems like English teachers can’t help themselves. Nor should they! It’s great advice, no matter what kind of story you’re writing. But just saying “Show, don’t tell” doesn’t always explain the problem, leaving writers thinking they’re showing when they’re still telling.

Instead of listing endless examples, let’s look at a few specific problems you’re trying to avoid in your writing. Knowing why you don’t want to tell makes the adage much easier to extrapolate from.

Repetition
One of the most common issues is authors who are showing and telling. For example, a character who desperately tries to explain her situation to the police suddenly stamps her foot and screams in a scene. The author doesn’t need to clarify that she’s frustrated; we get it. So the line:

She stamped her foot and screamed in frustration at the idiocy surrounding her.

isn’t necessary. We’ve just read a back-and-forth with her becoming increasingly frustrated (which we inferred through the dialogue). The action beat of stamping her foot and screaming doesn’t need to explain why. Well-written dialogue plus behaviors everyone can relate to are enough to convey the emotion. That kind of repetition isn’t wrong per se, but it clutters the text and demonstrates the author’s lack of confidence in their writing.

Narrative Distance
Another reason to focus on showing is that telling instills a greater narrative distance between the reader and the character(s). Plenty of other things affect narrative distance, such as point of view and tense. And again, this isn’t always a bad thing, but for many genres, it’s better to get the audience as close to the action as possible.

Looking at the line I used above again, the reader is somewhat removed from the situation. By explicitly noting that she’s frustrated, the author has inserted a narrator’s observations (even if the narrator isn’t a character and is omniscient). Consider the lines below.

She stamped her foot and screamed. The sheer idiocy was unbelievable!

There’s nothing separating the audience from the events described. You know what she’s doing and what she’s thinking without ever needing to spell out her emotions. The proceeding dialogue (hopefully) clearly showed this frantic woman explaining her situation over and over to an officer who, for whatever reason, wasn’t paying much attention. In a tense scene, you want to keep things moving.

Head Hopping
One of the biggest mistakes writers make from telling instead of showing is called head hopping. It’s most common in third-person limited POVs and happens when the reader is given direct insight into a character’s motivations or thoughts when they shouldn’t be.

Continuing my example, let’s say that we see the line in a book where the detective is the protagonist and his thoughts are the only ones shared with the reader.

She stamped her foot and screamed in frustration at the idiocy surrounding her. Detective Tanner politely averted his eyes, not wanting to make things worse.

While it’s possible that the detective figured out she was frustrated and assigned that emotion to her actions, when the narrator explicitly states it is because of her perception of idiocy, they’ve hopped into the woman’s head. Detective Tanner has no way of knowing for sure where her frustrations lie. The detective isn’t thinking here; the narrator is telling us.

Have Some Faith
While it’s usually best to give your writing (and your audience) a little credit, authors occasionally still want to show and tell. One way to do this is by having the protagonist do the telling.

She stamped her foot and screamed. Detective Tanner politely averted his eyes from the hysterics, not wanting to contribute to her obvious frustration.

Here, we see the action and the detective’s assumptions: that she’s acting out of frustration and it's unwarranted. This neatly avoids hopping into the woman’s head while also giving us some characterization of Detective Tanner. Like all tricks, you don't want to overuse it. No one wants to constantly have the protagonist weighing in like this on every action, but it is effective in moderation.